1. Field of the Invention
The present invention is generally concerned with reading off the contour of the rims or surrounds of an eyeglass frame as usually carried out in order to match to the latter the eyeglass lenses to be mounted therein.
The contour is usually read off by means of a device equipped with an appropriate sensor or feeler.
2. Description of the Prior Art
A contour reading device of this kind is described in U.S. Pat. No. 5,121,548, for example.
In the above patent the eyeglass frame from which the contour is to be read off is held fixed and the feeler includes a head to be inserted into the bezel of the rim or surround concerned at the end of a rod. This head is mobile and its position is systematically defined in a particular system of coordinates.
This example uses polar coordinates in a plane perpendicular to the rod of the feeler plus an altitude in the direction perpendicular to this plane to allow for the menisci of the more usual eyeglass frame rims or surrounds.
At present, as in the patent mentioned above, contour reading is essentially concerned with the circumferential contour of the rim or surround of the eyeglass frame being measured.
However, no account is taken of the actual profile of the bezel of this rim or surround, i.e. the cross-section of the bezel.
This cross-section can be dihedral or of any other kind, for example half-round; moreover, there is in practise a great diversity of bezel cross-sections from one eyeglass frame to another, depending on the manufacturer.
Given the inevitable manufacturing tolerances of the grinding wheels used to cut the corresponding bead on the edge of an eyeglass lens, which is traditionally called a bevel even when its cross-section is not dihedral, and the wear to which such grinding wheels are inevitably subject in time, it is by no means rare to observe discrepancies between the cross-section of the bevel of an eyeglass lens and that of the bezel of the eyeglass frame rim or surround in which the latter is to be mounted that are sufficiently great to compromise the proper retention of the eyeglass lens in the rims or surrounds of the eyeglass frame.
When cutting a bevel on the edge of an eyeglass lens it is therefore desirable to make the maximum allowance for the actual cross-section of the bezel of the eyeglass frame rim or surround in which the eyeglass lens is to be mounted.
In U.S. Pat. No. 5,450,335 it is assumed that the angle of the cross-section, which is dihedral in this example, is known.
The present invention consists in a method for effectively reading of this cross-section; the invention also consists in a feeler for implementing this method.